A Study to Find the Dose and Assess the Immune Response and Safety of a Vaccine Against Influenza in Healthy Younger and Older Adults

1 dose of Flu mRNA Formulation 1 is administered intramuscularly in the non-dominant upper deltoid to YA participants at Day 1.

1 dose of Flu mRNA Formulation 2 is administered intramuscularly in the non-dominant upper deltoid to YA at Day 1.

1 dose of Flu mRNA Formulation 3 is administered intramuscularly in the non-dominant upper deltoid to YA participants at Day 1.

1 dose of Flu mRNA Formulation 4 is administered intramuscularly in the non-dominant upper deltoid to YA participants at Day 1.

1 dose of Flu mRNA Formulation 5 is administered intramuscularly in the non-dominant upper deltoid to OA participants at Day 1.

1 dose of Flu mRNA Formulation 6 is administered intramuscularly in the non-dominant upper deltoid to OA participants at Day 1.

1 dose of Flu mRNA Formulation 7 is administered intramuscularly in the non-dominant upper deltoid to OA participants at Day 1.

1 dose of Flu mRNA Formulation 8 is administered intramuscularly in the non-dominant upper deltoid to OA participants at Day 1.

1 dose of active comparator 1 is administered intramuscularly in the non-dominant upper deltoid to YA participants at Day 1.

1 dose of active comparator 2 is administered intramuscularly in the non-dominant upper deltoid to OA participants at Day 1.

1 dose of Flu mRNA Formulation 9 is administered intramuscularly in the non-dominant upper deltoid to YA participants at Day 1.

1 dose of Flu mRNA Formulation 10 is administered intramuscularly in the non-dominant upper deltoid to OA participants at Day 1.

1 dose of active comparator 3 is administered intramuscularly in the non-dominant upper deltoid to YA participants at Day 1.

1 dose of active comparator 4 is administered intramuscularly in the non-dominant upper deltoid to OA at Day1.